This invention relates to a hydrocyclone for dividing a liquid-solid suspension into an accept and a reject portion.
Hydrocyclones are used in the purification of fluid-particle suspensions, with particular application to liquid-fiber suspensions such as in the manufacture of pulp and paper products. The liquid-fiber suspension, including contaminants, enters the hydrocyclone under pressure through a tangential feed inlet. A rotational motion is imparted to the liquid-fiber-contaminants suspension as it enters the separation chamber, which consists, in part, of a conical portion. The rotational motion of the suspension causes a separation of the contaminants from the acceptable fiber. The contaminant portion of the suspension, which may contain dirt and metal particles, fiber bundles and other heavy debris, separates out to the wall of the separation chamber due to centrifugal action and is carried along the wall of the separation chamber to the conical portion of the chamber. As the conical portion converges, the centrifugal action increases causing a concentration of contaminants along the inner wall as the reject outlet is approached. The reject portion of the suspension, along with some acceptable fiber, exits the hydrocyclone through the reject outlet at the apex of the conical section of the separation chamber. The acceptable portion of the suspension exits the hydrocyclone axially along the center line of the separation chamber, to an accepts outlet which may be either axial or tangential to the separation chamber.
The high velocity and abrasive nature of the contaminants within the hydrocyclone can cause wear of the separation chamber, most noticeably in the conical section. This wear can, over time, progress to a degree as to form an aperture in the conical section and permit the suspension to leak from the hydrocyclone. In this event, a shutdown of the hydrocyclone and possibly of associated equipment would be necessary in order to replace this component of the separation chamber. This shutdown operation can be very costly. Excessive wear can also create an unsafe condition in which sudden failure of the separation chamber due to weakened wall sections of the chamber could release the pressurized suspension.
The prior art includes hydrocyclones having chambers exterior to the separation chamber into which a leak would flow before reaching the exterior of the hydrocyclone filling the enclosed space. The chambers can eventually become filled with contaminant particles and fibers plugging the leak and making it impossible for operators to detect the leak, rendering the chamber functionless. U.S. Pat. No. 4,278,534 to Jakobson describes a hydrocyclone having the above mentioned outer chamber wherein a leak originating from an aperture in the separation chamber caused by abrasive wear will result in flow to the outer chamber and not to the exterior of the hydrocyclone. U.S. Pat. No. 4,358,369 to Matula et al. describes a hydrocyclone having an outer chamber including an axial "strip" of reduced wall thickness on the wall of the separation chamber, thereby localizing the area in which an aperture will develop. The abrasive particles initially wear through the strip and fluid flows into the outer chamber. This patent describes two solutions: either the outer chamber is constructed from a clear material allowing for the leakage to be detected by sight, or the outer chamber itself contains an aperture from which a leakage will flow into ambient space. The aperture created can be sealed with a screw plug. U.S. Pat. No. 4,211,643 to Frykhult et al. describes a hydrocyclone having an outer chamber surrounding the separation chamber wherein the outer wall includes a plurality of sealable openings. A leakage in the separation chamber will be detected when the fluid is observed flowing from the apertures into ambient space. The leakage can be arrested by using a sealing device.